Electronic self-destruct device

ABSTRACT

A device provides for time-controlled self-destruction of a projectile by a batteryless, electronic self-destruct device. Several capacitors charged by a piezo element or a surge generator during firing are used in the flight phase for operational purposes. At least two of the capacitors are connected to the input of a comparator, so that the influence of a constantly modifiable operational voltage and the influence of a discharge of modifiable voltage levels by the piezo element or surge generator does not affect the time function.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a configuration for an electronicself-destruct device in a projectile detonator without the use of abattery installed in the detonator.

2. Description of the Related Art

Apart from the main detonation criteria, such as impact or timefunction, for today's projectile or submunition detonators frequently aself-destruction function is also demanded, which also ignites theexplosive in the absence of a response of the primary ignition criteriaafter the passage of a maximum function time. This function, parallel tothe other ignition criteria, is intended to limit the danger range ofthe munition in the firing direction and/or minimize the occurrence ofdud shots. This makes utilization in previously conquered territoriessafer due to the lower danger through one's own duds. This function alsopermits, on the other hand, the bombardment of an encircled enemywithout endangering opposing troops of one's own or civilianinstallations beyond a justifiable degree.

SUMMARY OF THE INVENTION

Mechanical, pyrotechnical and electronic self-destruct devices are knownin different implementations. The present object is based on therequired operation of an electronic self-destruct device without using abattery. This has the advantage that the self-destruct function ofdetonators thus equipped is retained highly reliably even over a longstorage time of the detonator, since the reliability of detonatorfunctions is essentially a function of the reliability of the energysupply. The reliability of the self-destruct function, however, overtactical deployment is not only critical to function, but also tosafety. For that reason, all structural elements impairing thefunctional reliability should be eliminated as much as possible.

Building on this prior art, the present invention therefore has as itsobject specifying a new configuration with the self-destruct function,specifically of projectile detonators, which operates without a battery.

Utilizing for the electric operation of the self-destruct device theelectric energy of one or several piezo elements is known. During thefiring process, due to the high acceleration occurring, the piezoelement outputs for a time period of a few milliseconds a high voltagewhich for longer-duration operation of a current-saving electroniccircuitry is transferred with changed voltage level into storagecapacitors.

The problem of such an energy supply lies in the case of utilization ofthe electronic circuitry for the realization of a highly precise timefunction. Although the supply voltage change is of extreme magnitude,the energy supply capacitors are only charged through the firing, andsubsequently are continuously discharged through the current to besupplied by the capacitors. For reasons of cost and reliability, thetime function is to be realized with RC networks instead of bymechanical oscillators, such as a quartz [oscillator] or a resonator,which can be damaged during the firing. However, the oscillationfrequency of RC oscillators is highly dependent on the operating voltagesuch that application for a self-destruction, in general, is notpossible.

It would be possible to stabilize the output voltage of an energystorage capacitor with the aid of a switching regulator in order toprovide for the electronic circuitry a voltage as constant as feasible.However, this has the disadvantage of a relatively large circuitexpenditure connected with energy losses through the voltage changer.

A second solution would be to employ the output voltage of the piezoelements for the realization of the time function, to charge a capacitorC to a voltage U_(o) and to discharge the capacitor C via a resistanceR, in order to detect with the aid of a comparator if a voltage levelU_(S) falls below a specific level which occurs after timet _(S) =−R C ln(U _(S) /U _(o))  (1)

After this time, the comparator output changes its state. This change isemployed for igniting a succeeding ignition thyristor, which dischargesan ignition capacitor, also charged separately by the piezo element,into an electric ignition means.

However, this solution entails the disadvantage of the dependence of theself-destruct time t_(S) on U_(o) and U_(S). Since piezo elements aresubject to fabrication fluctuations and are temperature dependent, thevoltage U_(o) can fluctuate from shot to shot and therewith also theself-destruct times. In addition, a stable switching threshold U_(S)with variable operating voltage, again requires circuitry expenditures,which lead to higher complexity and current consumption.

Therefore, a circuit is to be provided which, on the one hand, is ofmaximum simplicity and therefore as much as possible energy-saving,cost-efficient and at the same time (due to reduced number of structuralparts) is reliable and which, on the other hand, permits realization thetime function with RC networks independently of a fluctuating supplyvoltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, capacitors C0 to C4 are charged during the firing via a piezoelement P a voltage generator, a dropping resistor R0, a Zener diode Z(for voltage limitation) and diodes D0 to D3. Delayed across resistor R4and the second storage capacitor C3, the charged capacitor C0subsequently provides the supply voltage for the operation of acomparator K. The comparator K is a commercially available integrated[circuit] package with extremely low current consumption (<1 μA), verylow input currents (<pA) and a common mode range extending up to thelimits of the operating voltage.

The delayed provision of the operating voltage is to prevent amalfunction during the barrel passage phase and the capacitor C3 chargedwith delay supplies at the point in time of the ignition the energy fordriving the thyristor Th. The ignition capacitor C4 is charged acrossdiode D3, and remains at a sufficient voltage level until the ignitionof the thyristor Th. For realizing a time function independent of thevoltage output by the piezo element P, according to the invention, thetwo capacitors C1 and C2 are charged, via the two high-blocking diodesD1 and D2, by the piezo element P to the same voltage U_(o).

Capacitor C1 is connected to the positive input of comparator K across avoltage divider R1 and R2. Capacitor C2 is connected directly to thenegative input of the comparator K and is discharged across resistor R3after the firing.

For the rapid and reliable switching over, the comparator K is connectedthrough positive feedback across resistor R5 and thus has hysteresis.After the firing, due to the voltage divider R1 and R2 at the minusinput of comparator K, a higher positive voltage is present than at theplus input. The output of the comparator K is therefore at this point intime at zero potential. Capacitor C1 is subsequently discharged acrossthe equivalent resistance R_(e)=R1+R2* with R2*=R∥R5=R2 R5/(R2+R5).

Time constants T_(1=R) _(e) C1 and T₂=R3 C2 are selected such thatT₁>T₂, i.e., C2 is discharged faster than C1. At the point in time ofthe self-destruct time sett _(S) =T ₁ T ₂/(T ₂ −T ₁)ln(R 2 */R _(e))  (2)the potential at C2 (at the minus input of comparator K) falls below themore slowly changing potential of C1, reduced by the factor R2*/R_(e),at the plus input of comparator K. The comparator K subsequentlyswitches its output voltage to positive potential and therewith ignitesthe ignition thyristor Th across the current limitation resistor R6 andthe voltage divider R7 and R8. Capacitor C5 serves for disturbancesuppression and is of no significance for the function principle.

The energy stored in ignition capacitor C4 is thereby switched throughto electric ignition means EZ and the latter is made to trigger. Acrossthe depicted input T, thyristor Th can also be ignited via the mainignition criteria by circuit parts not shown here.

A further simplification of the circuit and the calculation is obtainedif the capacitors C1 and C2 are of equal value: C1=C2=C. Theself-destruct time tS is thent _(s) =R _(e) C/(1−R _(e) /R 3)ln(R 2 */R _(e))  (3)which means that it can be adjusted nearly linearly within wide rangesby solely changing the resistance R3.

Through the difference formation of the present comparator circuitry noparameter variable is included in either equation (2) nor equation (3)during firing. The goal of the task consequently has been attained.

A changed field of application of the circuit is opened up if thecharging of the capacitors C0 to C4 is carried out by a piezo elementduring the firing through a voltage in a warhead, which is eitherpermanently applied or is generated shortly before the ejection ofsubmunition under control by a warhead is electronic circuitry. Thecircuit in this case serves for the time-controlled triggering of aself-destruction of the ejected submunition. As long as board voltage isapplied, neither C1 nor C2 is discharged and nothing occurs at thecomparator output. Only when the voltage supply is cut off (ejection ofthe submunition) is the self-destruct configuration activated; thecapacitors C1 and C2 start discharging and, as described, initiate theignition process.

Instead of the piezo element employed in connection with the embodimentexample, a surge generator can also be utilized. In this case, in FIG.1, the piezo element P would need to be replaced by a surge generatornot depicted.

1. An apparatus for time-controlled self-destruction of a projectile,said apparatus comprising: a voltage generator operable to generate avoltage during firing of the projectile; a plurality of capacitorsoperable to be charged by the voltage generated by said voltagegenerator; a voltage divider including a first resistor and a secondresistor; a comparator having a first input and a second input, whereinat least a first capacitor of said plurality of capacitors is connectedvia said voltage divider to said first input and at least a secondcapacitor of said plurality of capacitors is connected to said secondinput, and said first and second capacitors are adapted to be chargedequally by the voltage generated by said voltage generator; and a thirdresistor connected in parallel with said second capacitor, wherein aresistance of said third resistor is higher than a sum of a resistanceof said first resistor and a resistance of said second resistor.
 2. Anapparatus as recited in claim 1, wherein said first input of saidcomparator is a positive input and said second input of said comparatoris a negative input.
 3. An apparatus as recited in claim 1, furthercomprising a fourth resistor connected between said first input of saidcomparator and an output of said comparator, wherein said fourthresistor forms a feedback loop for said comparator.
 4. An apparatus asrecited in claim 1, wherein said voltage generator is one of a surgegenerator and a piezo element.
 5. An apparatus as recited in claim 1,wherein said first and second capacitors have equal capacitances.